The invention relates generally to integrated circuit fabrication and semiconductor devices and, in particular, to fabrication methods and device structures for a bipolar junction transistor.
Bipolar junction transistors are found, among other end uses, in high-frequency and high-power end use applications. In particular, bipolar junction transistors may be used in microwave power amplifiers used in wireless communications systems and power amplifiers in mobile devices, as well as high-speed logic circuits.
Bipolar junction transistors are three-terminal electronic devices that include semiconductor regions defining an emitter, an intrinsic base, and a collector. An NPN bipolar junction transistor includes two regions of n-type semiconductor material constituting the emitter and collector, and a region of p-type semiconductor material constituting the intrinsic base situated between the two regions of n-type semiconductor material. A PNP bipolar junction transistor includes two regions of p-type semiconductor material constituting the emitter and collector, and a region of n-type semiconductor material constituting the intrinsic base situated between the two regions of p-type semiconductor material. The emitter, intrinsic base, and collector define a pair of p-n junctions, namely a collector-base junction and an emitter-base junction, across which the conductivity type of the respective semiconductor materials changes. A voltage applied across the emitter-base junction controls the movement of charge carriers that produces charge flow between the collector and emitter.
Improved fabrication methods and device structures are needed for a bipolar junction transistor.